Compressor power recovery

ABSTRACT

The three stage centrifugal compressor of the present invention employs a one-piece cast casing having a cylindrical bore containing therein a removable barrel assembly, which assembly comprises three directly engaging clamped diaphragms, three diffusers, three shrouds and a rotor having three impellers, all in axially stacked relationship. Fluid passages are provided integrally cast in the diaphragms and casing for conducting the fluid between stages and from the last stage to a use connection, monitoring devices and a feedback line to the first stage nozzles for partially operating the first stage as a turbine. For starting, a valve in the feedback line is opened so that the first stage operating as a partial turbine will reduce the starting time and power required. On partial load, for example, the output pressure will rise to again open the feedback line valve to reduce power consumption.

United States Patent Pilarczyk 1451 Aug. 1, 1972 [54] COMPRESSOR POWERRECOVERY FOREIGN PATENTS OR APPLICATIONS [72] In n r: K r Pilarczyk,Loudonville, NY. 536,890 5/1941 Great Britain ..415/53 [73] Assignee: mcurporafion Syracuse NY 1,070,496 12/1959 Germany ..415/53 [22] Filed:June 8, 1970 Primary Examiner-Henry F. Raduazo Attorney-Harry G. Martin,Jr. and J. Raymond Cur- [21] Appl. No.. 44,463 tin 52 US. 01. ..415/53,415/1 16, 415/146, 15 1 AB TRAC 415,179 The three stage centrifugalcompressor of the present [51] Int.Cl ..F04d 27/00, F04c 29/04, F04d17/08 invention employs a one piece cast casing having a Fleld of Search"415/ l 1 l6, cylindrical bore containing therein a removable barrel415/146, 1316- l assembly, which assembly comprises three directlyengaging clamped diaphragms, three diffusers, three References Citedshrouds and a rotor having three impellers, all in axially stackedrelationship. Fluid passages are provided UNITED STATES PATENTSintegrally cast in the diaphragms and casing for con- 1,915,997 6/1933Hoffmann ..415/116 ducting the fluid between Stages a m the last 2380,606 7/1945 Moody ..415/1 Stage a connecnonr momtonng devlces and a 2656 096 10/1953 Schwarz ..4l5/DIG. 1 feedback line the first Stage mulesPartially 2'660366 11/1953 Klein et al 415/53 operating the first stageas a turbine. For starting, a 2826l47 3/1958 Gauba'tz "415/53 valve inthe feedback line is opened so that the first 2785634 3/1957 i'' 'g5/143 stage operating as a partial turbine will reduce the 28500299/1958 Off d t l 415/10 starting time and power required. On partialload, for 3004494 10 1961 C e 5/143 example, the output pressure willrise to again open 3217'655 I 151965 g y g 'g "f "415/1 1 6 the feedbackline valve to reduce power consumption. 3:462:071 8/1969 Garve ..415/116 7 Claims, 6 Drawing Figures MSKKMK PATENTEUAUG H972 3.680.973

sum 1 BF 3 'mmm fr? vent-or- ,far'a/ /larcayle PATENTEDAUG 1 m2 3.680,973 sum 3 or 3 mvnmon KARoL PILARCZYK ATTORNEY BACKGROUND OF THEINVENTION Power recovery for multi-stage compression that employspressure responsive valved feedback lines are known, for example in theUS. patents to Moody US. Pat. NO. 2,380,606 and Alberger US. Pat. NO.1,009,819. However, the needs for improved efficiency, decreasedmanufacturing costs, compactness and versatility are always present.

CROSS-REFERENCING TO RELATED APPLICATIONS The features of the inventionof this application may be used in combination with the features of theinventions in applicants following related applications of the samefiling date and assignee as the present application, the disclosures ofwhich are incorporated herein in their entirety by reference: CompressorBarrel Assembly, Ser. No. 44,446; Variable Capacity Compressor, Ser. No.44,263; Interchangeable Compressor Drive, Ser. No. 44,403; compressorBase and Intercoolers, Ser. No. 44,034 now issued as US. Pat. No.3,644,054.

SUMMARY OF THE INVENTION It is an object of the present invention toimprove multi-stage compressor efficiency, compactness and versatilitywhile lowering manufacturing costs, with respect to compressor powerrecovery by feeding high pressure gas back to a lower stage employingimpeller tip nozzles under the control of a pressure responsive andindependently actuatable valve. The above is accomplished without aconsiderable amount of piping about the casing. The axial limitationswith respect to length are of considerable advantage in providing aminimum length to the cantilevered portion of an overhung rotor so thathigh speed operation may be possible. The piping connections betweenstages are cast into removable diaphragms and a one piece casing.

The removable barrel assembly includes a diaphragm, a shroud, a diffuserand an impeller for each stage. The feedback lines are cast into thecasing and diaphragms so that conversion to power recovery isaccomplished by drilling one shroud and inserting nozzles, and byproviding appropriate valving. The specific location of the nozzles withrespect to the lower stage impeller blade tips is an important featurefor efficien- BRIEF DESCRIPTION OF THE DRAWING Further objects, featuresand advantages of the present invention will become more clear from thefollowing detailed description of a preferred embodiment of the presentinvention as shown in the attached drawing, in which:

FIG. 1 is a perspective view of a complete compressor employing thefeatures of the present invention;

FIG. 2 is a schematic flow sheet showing the path of the fluid as itmoves between stages and through the intercoolers;

FIG. 3 is a partial cross-sectional view taken on a vertical planepassing substantially through the axis Of rotation of the compressor ofFIG. 1;

FIG. 4 is a side view of the first stage shroud;

FIG. 5 is an end view of the shroud of FIG. 4, looking toward the leftas seen in FIG. 3; and

FIG. 6 is a cross-sectional view taken along line 6-6 in FIG. 5. 0

DETAILED DESCRIPTION OF THE DRAWING With reference to FIGS. l-3, thecompressor base 1 securely mounts an electric drive motor 2, which hasan output shaft 3 for driving the rotor 4 through gear train 5. The geartrain 5 is mountedwithin a separate casing 6 that forms the end closurefor the compressor casing 7. The casings 6 and 7 are each cast in onepiece from iron, and the base 1 is a welded sheet steel fabrication.Inlet fluid is provided for the compressor through an inlet housing 8having mounted therein an inlet valve 9 controlled by a suitablemechanism 10.

Within the base 1, there are two separated intercooler chambers 11 and12 for cooling the fluid between the first and second stages and betweenthe second and third stages, respectively. For the purposes of thepresent invention, these intercooler chambers may be of any constructionand include any type of conventional intercooling equipment, such as aparallel tube water-gas heat exchanger. As shown in FIG. 2, inlet fluidpasses through the first stage impeller 13, the intercooler chamber 11,the second stage impeller 14, the intercooler chamber 12, the thirdstage impeller 15.

As shown in FIGS. 1 and 3, the cast iron casing 7 is provided with anaxial cylindrical bore 16 and a planar surface 17, with a plurality ofintegrally cast passages therebetween for conducting the fluid betweenstages and the intercoolers. Particularly, passage 18 conducts fluidfrom the first stage output to the intercooler chamber 11, passage 19conducts fluid from the intercooler charnber l l to the second stage,passage 20 conducts fluid from the second stage to the intercoolerchamber 12, and passage 21 conducts fluid from the intercooler chamber12 to the third stage.

In FIG. 3, a three stage removable barrel assembly is shown within thecylindrical bore of the casing 7, although according to the broaderaspects of the present invention any number of stages may be employed.The first stage includes a diaphragm 22, a shroud 23, a diffuser 24 andthe impeller 13; the second stage includes diaphragm 25, shroud 26,diffuser 27, and impeller 14; and the third stage includes diaphragm 28,shroud 29, diffuser 30, and impeller 15. Each of the diaphragms is a onepiece iron casting, and each of the diffusers and shrouds is a one piecealuminum casting. Each of the diaphragms 22, 25, 28 has an outercylindrical surface in direct engagement with the inner cylindrical bore16 of the casing 7. The end closure formed by the gear casing 6 has anadjacent inner cylindrical surface 31 that is flush with the cylindricalsurface 16 of the compressor casing 7, with the outer cylindricalsurface of the diaphragms 25 overlapping these flush inner cylindricalsurfaces to accurately align the gear casing 6 with the barrel assemblyfor proper positioning of the rotor 4. The gear casing 6 determines thepositioning of the rotor 4, by means of the radial bearing 32 and thecombination radial-thrust bearing 33 that rotatably mount the rotor 4 inan overhung position. The rotor may be of any rigid type construction,but preferably the impellers l3, l4, 15 are integrally secured to therotor shaft, with the interposition of suitable labrinth seals as shown.

In assembling the barrel assembly, the various components are assembledoutside the casing and slid from left to right, as viewed in FIG. 3,into the casings 6 and 7. Thereafter, the diaphragms 22, 25, 28 arerigidly secured to the gear casing 6 by means of a plurality of tensionbolts 34.

The shrouds 23, 26, 29 and diffusers 24, 27, 30 radially engage thediaphragms to fix their radial position and axially engage, in only onedirection, the diaphragms to fix their axial position while allowingfree axial play or clearance movement in the opposite axial directionwith respect to the diaphragms. This axial free play is taken up bybiasing means including the axially compressed sealing O-rings 36, 37and the piston action of the surfaces exposed to the pumped fluid on thediffusers and shrouds. Thus, the advantages of providing separateshrouds and separate diffusers with respect to manufacturing proceduresand replacement for power recovery conversion are provided without alsoproviding the heretofore correlated disadvantages of toleranceaccumulation.

From FIG. 3, it is seen that the previously described passages l8, 19,20, 21 are in communication with annular chambers 38, 39, 40, 41,respectively, formed by opposed outwardly opening annular channels onthe outer surfaces of the diaphragms 22, 25, 28, and inwardly openingannular channels axially spaced along the bore 16 of the compressorcasing 7. These annular chambers 38-41, are sealed with respect to eachother by any appropriate means, for example, O-rings (not shown). Thediaphragms 22, 25, 28 are provided with integrally cast passages orexternally configurated surfaces cooperating with surfaces of adjacentdiaphragms to form passages for conducting fluid between the annularchamber 38-41 and respective ones of the shroud inputs and diffuseroutputs.

In addition, the output from the last stage diffuser 30 is connected bythe diaphragms into the annular chamber 42 formed by opposed annularchannels in the diaphragm 25 and casing 7. From the annular chamber 42,the high pressure compressor output may pass upwardly through an outlet43, as shown in FIG. 1, to the point of use, storage tank,- conventionalblow-off device, or the like. Also, the compressor output may beconducted from the annular chamber 42 downwardly into the compressorbase 1 to be connected to piping to the point of use and/or be connectedto various pressure responsive control and monitoring devices, which forexample may have meters, warning lights or the like on the control panel45 as shown in FIG. 1. Also, in FIG. 1, the outlet 43 is shown with asealing plug or cap that is used when'an excess pressure blow-off deviceis not employed and the compressor output is directed downwardly intothe compressor base for connection with piping to the point of use.Further, the compressor output from annular chamber 42 is conducted bymeans of a generally axially extending passage that is cast into thecasing 7, but not in communication with any of the previously describedpassages of the casing 7, which passage conducts a portion of thecompressor output to annular chamber 47, which is shown in FIG. 3 asbeing formed-by opposed annular channels respectively in the casing 7and diaphragm 22. From the annular chamber 47 the high pressurecompressor output is directed into an annular chamber 48 formed betweenthe shroud 23 and diaphragm 22. A plurality of nozzles 49 are insertedthrough the shroud 23 to direct the high pressure gases from chamber 48against the blade tips of impeller 13 to produce a power recoveryturbine action during starting and to take care of excess pressure onpartial load. This capacity is built into the compressor so that thechamber exists with a shroud 23 not provided with nozzles, and ifdesired, appropriate pressure responsive valving may be incorporatedinto the feedback passage for dumping excess pressure into the annularchamber 48, and the shroud 23 may be drilled for receptionof nozzles tocomplete the conversion of the basic compressor into the power recoverycompressor specifically shown in FIGS. 2-6. This capacity is built inwhether used or not.

From the above, it is seen that the compressor of the present inventionmay be sold as a multi-stage compressor without power recovery, but withthe power recovery piping integrally cast into the diaphragms and casingwithout extra cost so that conversion of the compressor for powerrecovery only involves removal and drilling of the shroud 23, theinsertion of nozzles in the drilled bores of shroud 23, and theinterposition of suitable valving controls in the feedback passage, aswill be set forth in more detail below.

While the power recovery principles of the present invention may be usedwith a compressor having any number of stages, the only requirement isthat compressed gas is fed back from a higher stage to a lower stage,either stage of which may be a terminal stage or intermediate stage, orcombinations thereof. Specifically, the disclosed compressor, providespower recovery from the output of the third stage impeller 15, as shownin-FIG. 2, through feedback line 50, to the first stage impeller 13,with the interposition of a valve 51. Preferably, the valve 51 is apressure responsive valve, that is, a valve normally spring biased inits closed position but which will open to allow passage of gas throughfeedback line 50 when a predetermined pressure is exceeded. Thus, duringthe operation of the compressor, if usage falls off so that the loaddrops and output pressure correspondingly increases, the pressureresponsive valve 51 will open to allow the output of the third stage tobe conducted back to the first stage to operate the first stage as apartial turbine to reduce the total input power required for thecompressor. It is known to have pressure responsive blow-off valves thatwill vent excess pressure into the atmosphere, but the present inventionprovides power recovery so that this excess pressure is utilized toreduce the total power needed to drive the compressor during partialload. Numerous pressure responsive valves are commonly available, sothat no specific valve has been disclosed.

During starting of the compressor, the power required for starting isreduced by connecting the starting circuit with a solenoid 52, so thatthe valve 51 will be open to allow pasage of compressed gas from thethird stage to the first stage during starting regardless of the outputpressure of the third stage. This will considerably reduce the startingtime, reduce the starting power required and correspondingly a smallerdrive motor may be employed. Preferably, thev solenoid 52 is connectedwith the valve 51 so that during normal operation of the compressor, thesolenoid is energized to hold the valve in its spring-biased closedposition in which it will operate as a pressure responsive valve.

This arrangement is desirable so that in the event of a power failurethat may interrupt operation of the various controls, the solenoid 52will be deenergized to automatically open the valve 51 so that theoutput pres sure of the third stage will not reach abnormally highlevels. Thus, the compressor will fail safe.

From the above, it is seen that the power recovery system of the presentinvention provides for safe failure, reduced starting time, reducedstarting power, and increased efficiency upon partial load.

As shown in FIGS. 4 6, the shroud 23 is provided with an axially alignedfirst drilled bore 53, an intermediate equal diameter or slightlysmaller diameter drilled bore 54, a smaller diameter inner drilled bore55, and an annular nozzle insert sleeve 56 received within theintermediate bore 54; all of which constitute a single nozzle assembly49. As seen particularly in FIG. 5, a plurality of these nozzleassemblies 49 is provided with equal spacing around the circumference ofthe shroud 23.

FIG. 5 is a view of the shroud 23 looking toward the left in the axialdirection of FIG. 3, so that reference line X is a diametric line, thatis, perpendicular to and intersecting the axis of rotation of the rotor4. Similarly, reference line Z is a radial line perpendicular to andintersecting the axis of rotation of the rotor 4. Line 6-6, on which istaken the cross section of FIG. 6, extends through the axis of symmetryof the elements 53-56 of one of the nozzles and thus gives a referenceline for the projection of the jet passing through this nozzle. As seenin FIG. 5, line 66 forms an angle of approximately 57 with a radial lineZ that passes through the nozzle output and forms an angle ofapproximately 33 with a line Y that passes through the nozzle outlet ina tangential direction, that is, perpendicular to line Z. Thus, it isseen that the jet issuing from this nozzle will have a velocitycomponent in the tangential direction and the radial outward direction.Each nozzle assembly is correspondingly constructed although the detailshave been given for only one to avoid duplication.

From FIG. 6, it is seen that the line of symmetry, that is the directionof the nozzle jet, forms an angle of approximately 25 with a planeperpendicular to the axis of rotation of rotor 4. Thus, the jet for eachnozzle also has an axial component of velocity.

From the above specific description of FIGS. 4-6, it is seen that theaxial cross-sectional view of FIG. 3 has been broken away along the axisof symmetry of respective nozzles 49, for purposes of clarity inillustrating the relationship of the nozzle assemblies 49 with a chamber48 and first stage impeller 13.

The compressor of the present invention is manufactured as a standarditem without the power recovery feature, and at the time of ordering orat any later date it may be converted for power recovery. However, as astandard manufactured item, the annular output chamber 42 of the thirdstage is connected by a cast passage in the casing 7, which leads to theannular chamber 47, which annular chamber 47 is directly connected withthe annular chamber 48 as shown in FIG. 3. Thus, the standard compressorwithout power recovery will provide feedback of high pressure gas to theannular chamber 48, where it will be contained and thus have no effectupon the compressor output. These feedback passages and chambers willnot materially increase the cost of the basic compressor, but willgreatly facilitate conversion to power recovery at any time, bycompletely eliminating the subsequent need for external piping.

To convert the compressor to power recovery, it is only necessary toremove the nut and washer on the bolt 34, the diaphragm 22 and theshroud 23. This will in no way disturb the mounting of the rotor 4 orthe other elements of the barrel assembly. After the removal of theshroud 23, it is bored as shown in FIGS. 4-6, and thereafter providedwith the nozzle inserts 56, which are converging type nozzles.Thereafter, the shroud 23, diaphragm 22 and nuts for bolts 34 arereassembled. As mentioned above, an integrally cast passage in thecasing 7 extends from the annular chambers 42 to the annular chamber 47.Access to this passage for the insertion of the valve 51 may be obtainedby drilling inlet and outlet bores, along with an intermediate plugbore, so that the plug bore may be used to block the through passage offluid and the valve 51 may be inserted between the inlet and outletbores. Further, it is contemplated that the standard compressor may onlyhave short cast passages in the casing 7, respectively in communicationwith the annular chambers 42 and 47, but not in communication with eachother; that is, with this modification, there would be no fluidconnection between the chambers 42 and 47 in the standard compressorwithout power recovery. The mounting of the valve for this modificationwould require separate tapping of these passages with the insertion ofthe valve between the taps. In any event, an important feature of thepresent invention is the integral casting of internal passages for powerrecovery, and the interposition of the valve 51 may take on many formswith the above teachings.

When starting the compressor, the solenoid 52 is automaticallydeenergized so that the valve 51 will be held in its open position.Thus, the output of the last stage will be conducted back through thefeedback passage 50, which includes chambers 42, 47 48, to the nozzleassemblies 49 so that high pressure jets of gas will be directed againstthe outer tips of the blades on impeller 13. In this manner, theimpeller 13 will partially operate as a turbine and simultaneouslyoperate as the first stage of a multi-stage compressor. Thus, the outputpressure will be reduced and power will be recovered in the first stagedue to the turbine action so that the total power requirements for thecompressor will be greatly reduced during start up. Since a drive systemgenerally consumes its greatest amount of power during start up, thesystem will have the advantage of permitting a smaller and less powerfuldrive system to be employed.

During normal operation of the compressor, there will be periods whenthe demand for compressed gas will be reduced or temporarily halted. Theshut down and start up of a compressor during these times is mostunsatisfactory and it has been known to provide automatic pressureresponsive valves for venting the compressor output to the atmosphere toreduce the power consumption. During these times, the valve 51 of thepresent invention will respond to this pressure build-up v to feed backhigh pressure gases to the first stage for the above-mentioned turbineoperation, which will reduce the power requirement in the same way as ablow-off valve and additionally reduce the power requirement by theamount of power recovered in the turbine.

In the event of a power failure during normal operation, which mightendanger the entire compressor system due to the shut down of variouscontrols, the solenoid 52 will automatically be deenergized so that thevalve 51 will automatically assume its open position to relieve theoutput pressure of the turbine and prevent excessively high pressures.

Since only the tips of the blades for impeller 13 are used for theturbine action, the impeller may be designed for efi'rcient compressorfunctioning, which as shown, takes on the preferred form of each bladehaving a radially extending inlet edge, an axially extending outletedge, a curved twisted intermediate edge caused by circumferentiallyoffsetting corresponding inlet and outlet edges. According to this typeof blading the tip portion of each blade extends generally radially andwill function quite well as a turbine blade with the arrangement ofnozzles as shown in FIGS. 4-6.

While a preferred embodiment of the present invention has beenspecifically illustrated, further modifications, variations andembodiments are contemplated according to the broader aspects of thisinvention.

What is claimed is:

l. A compressor, comprising: a one piece cast casing; a plurality ofseparate diaphragms, separate shrouds, separate diffusers and drivinglyconnected open bladed centrifugal impellers axially stacked within saidcasing to form at least two serially connected stages of compression;and said diaphragms and casing having integrally cast passage means forconducting discharge gas from the higher stage of compression to theside of the lower stage shroud opposite from its impeller.

2. The compressor of claim 1, wherein said lower stage of compressionshroud and diaphragm have cooperating surfaces forming an annularfeedback gas chamber exteriorly surrounding said lower stage shroud.

3. The compressor of claim 2, wherein said passage means includes saidlower stage diaphragm having integrally cast passage means extendingradially from said annular chamber to the inner bore of said casing,said casing and lower stage shroud having cooperating annular. channelsforming an annular chamber, said higher stage of compression diaphragmand said casing having cooperating annular channels forming an annularchamber, and said higher stage of compression diaphragm having integralpassage means extending between its annular chamber and said higherstage of compression diffuser.

4. A multi-stage compressor with a power recovery means comprising afirst open-bladed centrifugal impeller having an input and an output; asecond openbladed centrifugal impeller having an input and an output;means for driving said impellers; means connecting said impellers toconstitute said second impeller part of a higher pressure stage thansaid first impeller; gas feedback passage means for receiving highpressure gas from the output of said second impeller; nozzle means forreceiving high pressure gas from said feedback passage means anddischarging the gas directly against the o n bladin of said fi t im llerto decreas e energy output r epresente by LB: means for driviiig saidimpellers, said compressor including a stationarily mounted partitionclosely adjacent said first impeller, said partition having an innersurface facingsaid first open bladed impeller and an outer surfacefacing away from said first impeller, said nozzle means including apassage having a first bore extending inwardly from said second surface,and a second bore extending outwardly from said first surface andsmaller in diameter than said first bore; and a nozzle insert extendingbetween said bores.

5. A multi-stage compressor with power recovery means, comprising: afirst open-bladed centrifugal impeller having an input and an output; asecond openbladed centrifugal impeller having an input and an output;means for driving said impellers; means including a separate diaphragmfor each of said stages, a separate shroud for each of said stages, anda separate difiuser for each of said stages constituting nested axiallystacked fluid guide elements with said first impeller diaphragm andshroud forming therebetween an annular feed back chamber in fluidcommunication with a turbine nozzle means, connecting said impellers toconstitute said second impeller part of a higher pressure stage thansaid first impeller; gas feed back passage means for receiving highpressure gas from the output of said second impeller to said annularfeed back chamber; and turbine nozzle means in one of said annular feedback chamber forming members for receiving said high pressure gas fromsaid feedback passage means and said annular feed back chamber anddischarging the gas directly against the open blading of said firstimpeller to decrease the energy consumed for rotating said impellers bysaid driving means.

6. The compressor of claim 5, including a casing having a cylindricalinner bore receiving therein said diaphragms in radial engagement; saidcasing and first impeller diaphragm having integrally cast passagespartially forming said feedback passage; and said second impellerdiaphragm and said casing having integrally cast passage means at leastpartially forming said gas feedback passage means.

7. A multi-stage compressor with means power recovery, comprising: afirst open-bladed centrifugal impeller having an input and an output; asecond openbladed centrifugal impeller having an input and an output;means for driving said impellers; means connecting said impellers toconstitute said second impeller part of a higher pressure stage thansaid first impeller; gas feedback passage means for receiving highpressure gas from the outputof said second impeller; and nozzle meansfor receiving high pressure gas from said feedback passage means anddischarging the gas directly against the open blading of said firstimpeller to decrease the energy output represented by the means fordriving said impellers; control means regulating flow of gas in saidfeedback passage means including a normally closed first pressureresponsive control member and a second control member adapted to opensaid first member during start-up despite the absence of gas at apressure required to open said control member

1. A compressor, comprising: a one piece cast casing; a plurality ofseparate diaphragms, separate shrouds, separate diffusers and drivinglyconnected open bladed centrifugal impellers axially stacked within saidcasing to form at least two serially connected stages of compression;and said diaphragms and casing having integrally cast passage means forconducting discharge gas from the higher stage of compression to theside of the lower stage shroud opposite from its impeller.
 2. Thecompressor of claim 1, wherein said lower stage of compression shroudand diaphragm have cooperating surfaces forming an annular feedback gaschamber exteriorly surrounding said lower stage shroud.
 3. THecompressor of claim 2, wherein said passage means includes said lowerstage diaphragm having integrally cast passage means extending radiallyfrom said annular chamber to the inner bore of said casing, said casingand lower stage shroud having cooperating annular channels forming anannular chamber, said higher stage of compression diaphragm and saidcasing having cooperating annular channels forming an annular chamber,and said higher stage of compression diaphragm having integral passagemeans extending between its annular chamber and said higher stage ofcompression diffuser.
 4. A multi-stage compressor with a power recoverymeans comprising a first open-bladed centrifugal impeller having aninput and an output; a second open-bladed centrifugal impeller having aninput and an output; means for driving said impellers; means connectingsaid impellers to constitute said second impeller part of a higherpressure stage than said first impeller; gas feedback passage means forreceiving high pressure gas from the output of said second impeller;nozzle means for receiving high pressure gas from said feedback passagemeans and discharging the gas directly against the open blading of saidfirst impeller to decrease the energy output represented by the meansfor driving said impellers, said compressor including a stationarilymounted partition closely adjacent said first impeller, said partitionhaving an inner surface facing said first open bladed impeller and anouter surface facing away from said first impeller, said nozzle meansincluding a passage having a first bore extending inwardly from saidsecond surface, and a second bore extending outwardly from said firstsurface and smaller in diameter than said first bore; and a nozzleinsert extending between said bores.
 5. A multi-stage compressor withpower recovery means, comprising: a first open-bladed centrifugalimpeller having an input and an output; a second open-bladed centrifugalimpeller having an input and an output; means for driving saidimpellers; means including a separate diaphragm for each of said stages,a separate shroud for each of said stages, and a separate diffuser foreach of said stages constituting nested axially stacked fluid guideelements with said first impeller diaphragm and shroud formingtherebetween an annular feed back chamber in fluid communication with aturbine nozzle means, connecting said impellers to constitute saidsecond impeller part of a higher pressure stage than said firstimpeller; gas feed back passage means for receiving high pressure gasfrom the output of said second impeller to said annular feed backchamber; and turbine nozzle means in one of said annular feed backchamber forming members for receiving said high pressure gas from saidfeedback passage means and said annular feed back chamber anddischarging the gas directly against the open blading of said firstimpeller to decrease the energy consumed for rotating said impellers bysaid driving means.
 6. The compressor of claim 5, including a casinghaving a cylindrical inner bore receiving therein said diaphragms inradial engagement; said casing and first impeller diaphragm havingintegrally cast passages partially forming said feedback passage; andsaid second impeller diaphragm and said casing having integrally castpassage means at least partially forming said gas feedback passagemeans.
 7. A multi-stage compressor with means power recovery,comprising: a first open-bladed centrifugal impeller having an input andan output; a second open-bladed centrifugal impeller having an input andan output; means for driving said impellers; means connecting saidimpellers to constitute said second impeller part of a higher pressurestage than said first impeller; gas feedback passage means for receivinghigh pressure gas from the output of said second impeller; and nozzlemeans for receiving high pressure gas from said feedback passage meansand discharging the gas directly against the open blading of said firstimpeller to decrease the enErgy output represented by the means fordriving said impellers; control means regulating flow of gas in saidfeedback passage means including a normally closed first pressureresponsive control member and a second control member adapted to opensaid first member during start-up despite the absence of gas at apressure required to open said control member.